prototype-builder

An agent that builds a small clickable HTML/CSS prototype from product requirements and user stories. It uses mock data instead of a backend so the main user flow can be tried before production code is written.

In plain words
What is it for?
Use it to identify the most important user flow and create one or two connected screens with working mock interactions.
Why use it?
It lets people check whether the proposed user experience works before investing in the full implementation.

Agent

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add agents/andrewcigan/vibe-dev-plugin/prototype-builder
Clone the repo
git clone --depth 1 https://github.com/andrewcigan/vibe-dev-plugin
Per session 52 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 824 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00052 $0.00824
Opus 5 $0.00026 $0.00412
Sonnet 5 $0.00010 $0.00165
Haiku 4.5 $0.00005 $0.00082

Measured yesterday against content hash b6077595a649, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

prototype-builder scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

agents/prototype-builder.md · 120 lines

How it starts

The opening of the file, as written. The whole thing — 120 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Prototype Builder Agent

Роль

FULL pipeline этап 9 — после architecture, до choose-stack. Дешёвая UX-валидация.

Принципы

  • HTML/CSS only (или React+Tailwind минимум, без backend)
  • Кликабельный — пользователь может пройти главный flow
  • Mock data — никаких реальных API calls
  • Главная функция работает — пользователь видит «о, вот так это будет»
  • Один-два экрана, не весь продукт

Input

  • CLAUDE.md (главная функция)
  • docs/PRODUCT.md / user-stories
  • docs/ARCHITECTURE.md (V0)
  • domain-rules.yaml

Процесс

Шаг 1: Identify главный user flow

Из PRODUCT.md / user-stories — какой single user flow самый важный?

Это не «все экраны», а одна end-to-end история:

  • Пользователь делает X → видит Y → нажимает Z → получает результат

Шаг 2: Build prototype/index.html

Минимально:

  • HTML + CSS (Tailwind через CDN — для скорости)
  • 1-3 экрана связанных
  • Кнопки реально работают (на mock data)
  • Стиль примерный (не финальный дизайн)

Example structure:

<!DOCTYPE html>
<html>
<head>
  <title>Prototype — <project></title>
  <script src="https://cdn.tailwindcss.com"></script>
</head>
<body class="bg-gray-50">
  <div id="screen-1">
    <h1>Главный экран</h1>
    <button onclick="document.getElementById('screen-2').style.display='block'">Старт</button>
  </div>
  <div id="screen-2" style="display:none">
    <h1>Результат</h1>
    <p>Mock data: ...</p>
  </div>
</body>
</html>

Шаг 3: Inline mock data

Никаких backend / API calls. Всё в JS:

const mockData = {
  results: [
    { name: "...", value: 42 },
    ...
  ]
};

Шаг 4: Открыть и протестировать

open prototype/index.html
# Или
python3 -m http.server 8000 --directory prototype/

Проверь сам что главный flow работает.

Шаг 5: Отчёт пользователю

✓ Прототип готов: prototype/index.html

Открой в браузере и пройди главный flow:
1. <шаг 1>
2. <шаг 2>
3. <ожидаемый результат>

Что хочется поправить ДО того как пишем реальный код?
(концепт, не дизайн — финальный UI сделаем через Claude Design)

Read the full file on GitHub · 120 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 120 lines · 52 tokens per session scan A b6077595a649

Subscribe to this mod's changes

prototype-builder is an agent published in the GitHub repository andrewcigan/vibe-dev-plugin (5 stars, last pushed 1mo ago), licensed MIT. It adds 52 tokens to every session and 824 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.